Graphite joints of highly uniform electrical resistance



Dec. 15, 1964 E. c. THOMAS 3,151,580

GRAPHITE JOINTS OF HIGHLY UNIFORM ELECTRICAL RESISTANCE Filed Jan. 13,1961 2 Sheets-Sheet 1 Dec. 15, 1964 E. c. THOMAS 3,161,580

GRAPHI TE JOINTS 0F HIGHLY UNIFORM ELECTRICAL RESISTANCE Filed Jan. 13,1961 2 Sheets-Sheet 2 FIEA United States Patents 161 see GRAPE toners orrunner Urnronrr nrncrnrcar RESldTANtIE Edward C. Thomas, Lewiston, N.Y.,assignor to Great Lakes Carbon (Torporatmn, New York, N.Y., acorporation of Delaware Filed Jan. 13, 1961, Ser. No. 82,553 9 Qiaims.(Cl. fil h-288) bers may be low and the variations in same kept at aminimum.

It is well known that graphite anodes have been widely used inelectrolytic cells for such processes as decomposing brine solutions toproduce chlorine and caustic, etc.

In employing graphite anodes in electrolytic cells such as those ofthe-mercury cell type, it is customary to support the graphite anodesina horizontal plane by graphite pins which not only serve to mechanicallysupport the anode in the cell in the proper position but also serve toconduct electrical current from an external power supply to the graphiteanode. The anode plates vary in size depending upon the cell design butin general in a mercury cell, the anode assembly usually consists of arectangilar graphite plate mechanically supported and electricallyjoined to an outside power source by two graphite pins. More pins areemployed if the size of the anode plates used is increased. Several suchanode plates are employed in a single electrolytic cell;

In the operation of such electrolytic cells it is very desirable thatthe joint or connection between the pins and the anode plates not onlyhave sufficient mechanical strength to support the anodes during theiruseful life but also that the electrical resistance between each of theconnecting pins and the anodes be as low and at the same time as uniformas possible, throughout the entire cell. Unduly high resistances, ornumerous or wide variations in the electrical resistances of theseconnections or joints in the cell cause non-uniform deterioration of theanodes. The uneveness of wear and deterioration throughout the cellgives rise to complex operating problems, and requires much morefrequent adjustment and subsequent dismantling for repair orreconstruction of the cells than is or would be necessary if'each of thejoint resistances were uniformly low and fell within a narrow range ofvariation in resistance.

Other factors which should and must be considered in making these anodesand mounting them in the cells are the type of sockets employed in samefor mounting or receiving the support pins, the machining steps and costrequired to make such sockets, the facility with which the support pinsmay be assembled to the anodes, and the achieving of sufiicientmechanical strength at the joints in order that the pins give adequatesupport to the anodes suspended in the cells.

The conventional practice of coupling connecting pins to anodes is tothread the ends of the pins and to screw them into threaded sockets inthe anode. The types of threaded pins employed are generally three;viz., a pipe thread wherein the outer diameters of the threads are justa little less than the diameter of the main body portion of the pin, atapered thread wherein the diameter of the threads uniformly diminishesthe further the threads extend from the main body portion of the pin,and a shoulder type threaded pin which has a straight thread 3,l6l,5hPatented ec. 15, 1964 ice which is of a substantially smaller diameterthan the main body portion of the pin and wherein a shoulder is left onthe pin, the face of which shoulder is machined as ilat as possible andperpendicular to the threaded portion of the pin. This type of thread isusually provided with a loose tolerance, and when coupled to acorrespondingly threaded socket in an anode plate, graphite to graphitecontact is limited to only one side of the thread and to'theaforementioned shoulder on the pin. This particular type of jointdepends mainly upon electrical contact at the shoulder for itsconductivity. With all of these threaded types of joints and others, thecondition of the thread surfaces, both of the pins and of the socketsinto which the pins are to be threaded, has been found to be veryimportant. Tool chatter marks or high spots left on the threads resultin high and also uneven or non-uniform joint resistances. The jointresistances for these pins also vary considerably depending on theamount of torque employed to tighten them, the optimum amount employedvarying for each type of pin. The machining costs attendant upon usingthreaded pins are, therefore, high and the joint resistancesnon-uniform.

As an alternative to using. threaded pins, the art has partly turned toemploying a different type of joint between graphite connecting pins andanodes, namely interference or pressed joints. FIGURE 2 illustrates thistype of joint as well as the improvement of this invention, which willbe discussed in more detail hereinafter. These joints depend upon thefact that graphite is somewhat elastic or springy or pressure-compliantin nature and may be forced or compressed into sockets whose internaldiam eters are slightly less than the external diameters of the portionsof the pins forced into same. This difference in diameter, which may betermed interference should not be too great for if this occurs, theengaging portion of the pin or the socket of the anode begins to fail inits springiness. For example, for a 4 inch diameter pin, assembly forcesof approximately 700 pounds and 2400 pounds are typical forinterferences of 4 thousandths and 16 thousandths respectively. Theforce necessary to open or pull apart the joints is approximately equalto the closing force for interferences up to 12 thousandths. At 16thousandths interference, however, the force required to open the jointis from about 25% to about 50% less than the closingforce due toincipient flaws which had been induced in thesocket wall by excessivetensile strain or by other causes.

This type of joint, however, also has .somedisadvantages. Machiningtolerances for the external diameter of the engaging portion of the pinand for the internal diameter of the sockets are narrow because of therequirement of obtaining an interference falling within a fairly narrowrange, such as above-described. And even within this range theelectrical resistances of the joints vary considerably depending uponthe interference. In other words, the joint resistance for aninterference of four thousandths is appreciably higher than the jointresistance for an interference of twelve thousandths. This type ofjoint, therefore, although in many ways an improvement over threadedjoints in that the machining costs, joint resistances andvariations insame are reduced somewhat, still possesses these same disadvantages, buton a reduced basis.

It is an object, therefore, of this invention to produce graphite tometal or graphite to graphite couplings or joints wherein a high degreeof uniformity of electrical resistance between the members coupled oramong a series of such coupled members is obtained.

It is an additional object of this invention to accomplish the foregoingwhile maintaining low joint resistance.

It is an additional object of this invention to accom- 3 plish theforegoing while employing pressed-fit joints or couplings.

It is another object of this invention to accomplish the foregoing bymodifying the coupling pins, and particularly the engaging portionsthereof, which are employed in making such pressed-fit joints.

It is another object of this invention to accomplish the foregoing bymeans of a liquid-tight joint or coupling, between the graphiteconnecting pin and electrical conducting member to which it is coupled,when liquidtightness of the joint is of advantage or importance when theelectrical system of which the joint is a part, is in operation.

Most specifically, it is an object of this invention to provide meansfor mechanically supporting and coupling anodes in electrolytic cells toan external power supply wherein the resistances of the joints betweenthe coupling members and the anodes are low and of minimized variationin values and wherein the cost of machining the sockets of the anode,the facility with which the support pins may be assembled to the anodes,and the mechanical strengths of the joints all combine to make anoptimum system for minimizing construction and operational costs andmaximizing electrolytic cell life without the necessity of frequentrepair and adjustment.

It is a finding of this invention that the foregoing objects may beachieved by utilizing connecting pins in which there are means formaking the socket engaging portions of said pins more pressurecompliant, when coupled into sockets of the anodes or other typegraphite or metal members to which they are connected, than they wouldbe if no such means were employed.

The employment of such means for increasing pressure compliance in theengaging portions of the pins used in making pressed fit joints orconnections reduces the variations occuring in the electricalresistances of such joints and also permits much easier assemblage ofsuch joints by allowing looser production tolerances compared to the useof pressed fit pins having no means therein for increasing themechanical pressure complying characteristics of the pins. In otherwords, the employment of such means in such pins not only achieves anadditional degree of freedom when the pins are pressed into theanodesockets, permitting diametrical compression of the engaging portion ofthe pin in response to the compressive force imparted by the closefitting socket, but also reduces the undesired variations in theelectrical resistance of such joints, thereby obviating theaforedescribed disadvantages brought about by such variations. Theadvantageous mechanical compliance brought aboutby the use of such meansserves to reduce variation in tightness in the pin to socket assembly,thereby normalizing an otherwise pressure dependent, interferencedependent joint resistance.

The invention and its various features will become clearer afterconsideration of the attached drawings wherein:

FIGURE 1 is a top view of a pin coupled to an electrical conductingmember such as an anode plate;

FIGURE 2 is a vertical sectional view of the pinelectrical conductingmember of FIGURE 1 and is taken through the line 22 of said figure;

FIGURE 3 is an end view of the bottom of the pin of FIGURE 2;

FIGURE 4 is a vertical sectional View of another pinelectricalconducting member type of joint embraced within the present invention;

FIGURE 5 is an end View of the joint of FIGURE 4, taken along the line55 of said figure;

FIGURES 6 and 8 are bottom end views of connecting pins showing othermodifications of the invention;

FIGURES 7 and 9 are fragmentary vertical sectional views of the pins ofFIGURES 6 and 8 and taken along the lines 7-7 and 99 respectively ofsaid figures; and

FIGURE 10 is a vertical sectional view of a modifica- 4 tion of thepin-electrical conducting member type of joint shown in FIGURE 4.

All of the joints of this invention are characterized by the employmentof graphite connecting pins which are press-fitted by means ofunthreaded engaging portions into nonthreaded sockets in the electricalconducting mem bers to which the pins are coupled.

With reference to the figures, the pins may generally be described ascomprised of a main body portion 1, adapted (such as by means of athreaded well 8) for coupling to an external power supply, and anengaging portion 2 which is adapted to be press-fitted, or forcefitted,or frictionally engaged in non-threaded sockets of the members It) towhich the pins are coupled. The engaging portion of the pin is of ageneral cylindrical shape and in a preferred form is flared into andintegral with the main body portion of the pin, and chamfered at theperipheral edge of its face. It should be appreciated that the main bodyportion, though most conveniently circular in cross section, may also besquare, octagonal, etc, if desired, and that although itscross-sectional area will generally be greater than the cross-sectionalarea of the engaging portion, this is not essential to the practices ofthis invention, the dimensions of the engaging portion of the pin inrelation to the socket into which it is inserted being the importantconsideration.

Each of the pins also possess means within the engaging portion of thepin for making the engaging portion 2 more pressure compliant, as it isforced into the socket, than it would be if the means were absent. Themeans within the engaging portion for accomplishing this may be anannular kerf 3, typically from about to about ,5, inch wide, which issubstantially concentric with the circumference of the engaging portion,as is the case with the pin shown in FIGURES 2 and 3. Alternatively, itmay be a cylindrical hole 4 having a fiat base, or a modified type ofcylindrical hole 4a having a sloping base the centers of which holes areon the approximate axis of the pin, as with the pins of FIGURES 4 and 10respectively. Or the means may comprise three straight noncontiguous ornon-joining kerfs 5 of substantially equal length, none of which extendas far as the pins periphery, and which kerfs, if extended to intersectwith each other would approximately form an equilateral triangle, themiddle of each of the kerfs being substantially equidistant from theperiphery of the engaging portion of the pin, as with the pin of FIGURES6 and 7.

The means may also be shown in FIGURES 8 and 9 wherein three straightkerfs 6 of substantially equal length, none of which extends as far asthe periphery are also employed but which kerfs intersect with eachother to approximately form a triangle. As with the kerfs of FIGURE 6,the middle of each of these kerfs is substantially equidistant from theperiphery of the engaging portion of the pin.

In all cases the means employed for making the engaging portion morepressure compliant extends longitudinally from the bottom face of saidportion toward the main body portion. Because it is the engaging portiononly which takes part in the pressure fitting of the pin into thesocket, it may be unnecessary to extend the kerfs into the main bodyportion.

The greater the surface area of contact between the periphery of theengaging portion of the pin and the walls of the socket, the lower isthe resistance of the joint.' Thus the use of pins which are 5 inches indiameter results in less joint resistance than the use of pins 3 inchesin diameter. It follows from this that for any given size pin, it ispreferred that none of the kerfs, or means employed, to make theengaging portion of the pin more pressure compliant, cleave theperiphery of the engaging portion of the pin, for such cleavage reducesthe contact area between the pins and the socket, thus tending toincrease the joint resistance.

Such cleavege also, if it extends above the height of the socket,permits electrolyte to get between the pin and anode when the'jointsareused in electrolytic cells. This is undesirable because the effects ofeven the mild and inchoate electrolytic action which would take place inthe cavitacious confines of the joined members would tend to erode thegraphite structure much as it does at the bottom of the plate.Degeneracy of the graphite structure would ultimately lead to alooser-higher resistance joint.

And finally such cleavage tends to reduce the frictional engagementbetween the engaging portion of the pin and the socket walls thuslowering'or reducing the amount of force required to open or pull apartthe joints.

On the other hand, it may be possible to employ a kerf, either alone orin conjunction with the pressure compliant increasing means alreadydescribed, which cleaves the periphery at no more than one place. Thismight sometimes be resorted to in order to gain an additional degree ofpressure complying or an alternative manner for obtaining same, if itcan be done without too greatly adversely affecting the foregoingdiscussed properties sought for the joint. It is considered that anyperipheral cleavage more than this would detract more from the otherqualities sought or required for the joint than it would bring or add tosame in the way of increased pressure complying.

Therefore, no peripheral cleavage is preferred but a maximum of oneregion of peripheral cleavage may some times be resorted to whenpracticing the invention. The nature of the mechanical properties of aparticular type of graphite may also sometimes demand it. If pins havingsuch cleavage are employed in electrolytic cells, the kerf should extendno further from the bottom face of the pin than to within about 80-90%of the depth of penetration of the engaging portion of the pin into theanode socket, so that the liquid tightness of the joint is not impaired.In other words, it should extend longitudinally from the face of theengaging portion toward, but short of, the main body portion. This depthof penetration limitation is not required if the pin is employed whereliquid-tightness is not required, or where the pin has no peripheralcleavage.

With these qualifications, if a kerf is employed which cleaves theperiphery, it may typically be a radial slot extending out to theperiphery from the annular kerf of FIGURE 2. Or it might comprise asingle Archimedean curving kerf, one end of which extends out as far asthe peripheral contact surface.

The precise dimensions and locations of the kerfs or other meansemployed to make the engaging portions of the pins more pressurecompliant are not critical and may be varied widely within the spirit ofthe invention. Thus the diameter of the annulus 3 and its dimension arecapable of wide variation. So also are the diameters of the holes 4 and4a, or the distances of the kerfs 5 and 6 from the periphery of the pin.The only important factors limiting these variations are that theincreased pressure compliance desired should be obtained, therebyequalizing the contact forces of the engaging portion of the pin in thesocket, and that the mechanical stability of the pin in the socketshould not be impaired. By this latter point is meant that the kerfs orother means employed should not be so placed that the pins will snap orbreak when inserted into the sockets or when in prolonged use therein,and that the withdrawal forces of the pins from the sockets should notbe so reduced that the pins will become disengaged from the bodies towhich they are coupled. The desired results of this invention are easilyobtained despite these minor considerations which should be heeded andwhich will be obvious to one skilled in the art.

Although I have described my invention with a certain degree ofparticularity, it is understood that the present disclosure has beenmade only by way of example and that numerous changes in the details ofconstruction and the combination and arrangement of parts may beresorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

I claim:

1. In combination, a graphite pin electrically coupling an externalpower supply to an electrical conducting member having-a non-threadedsocket receiving an en gaging portion of said pin under compression,said pin being characterizedby having a main body portion coupled tosaidengaging portion and to an external power supply, saidengaging'portion being interiorly cut away to make it more pressurecompliant than said engaging portion would be if the interior cuttingwere absent, said cutaway portion extending longitudinally from the faceof the engaging portion in the direction of the main body portion andterminating within said graphite pin.

2. An electrical combination according to claim 1 wherein thenon-threaded socket of the electrical conducting member is cylindricalin shape and wherein the engaging portion of the pin is of a generalcylindrical shape flared into and integral with the main body portion ofthe pin, and chamfered at the peripheral edge of its face.

3. An electrical combination according to claim 1 wherein the interiorcutting which makes the engaging portion more pressure compliantcomprises an annular kerf substantially concentric with thecircumference of the engaging portion.

4. An electrical combination according to claim 1 wherein the interiorcutting which makes the engaging portion more pressure compliantcomprises three straight non-contiguous keris of substantially equallength, none of which extend as far as the periphery of said engagingportion, and which if extended to intersect with each other wouldapproximately form an equilateral triangle, the middle of each of thesekerfs being substantially equidistant from the periphery of saidengaging portion.

5. An electrical combination according to claim 1 wherein the interiorcutting which makes the engaging portion more pressure compliantcomprises three straight kerfs of substantially equal length, none ofwhich extend as far as the periphery of said engaging portion, and whichkerts intersect with each other to approximately form a triangle, themiddle of each of these kerfs being substantially equidistant from theperiphery of said engaging portion.

6. An electrical combination according to claim 1 wherein the interiorcutting which makes the engaging portion more pressure compliantcomprises a hole of a generally cylindrical shape, the center of whichhole is on the approximate axis of said pin.

7. An electrical system for use in an electrolytic cell comprising incombination a graphite anode having a non-threaded socket adapted toreceive an engaging portion of a graphite coupling pin undercompression, and a graphite coupling pin frictionally engaged in saidsocket, said pin being characterized by having a main body portioncoupled to said engaging portion and to an external power supply, saidengaging portion being interiorly cut away to make it more pressurecompliant than said engaging portion would be if the interior cuttingwere absent, said cut away portion extending longitudinally from theface of the engaging portion in the direction of the main body portionand terminating within said graphite pin, and said engaging portion alsohaving a peripheral cleavage extending inwardly to said cutaway portion,said peripheral cleavage being completely surrounded by and lyingentirely within said socket.

8. An electrical system for use in an electrolytic cel comprising incombination a graphite anode having 2 non-threaded socket adapted toreceive an engaging por tion of a graphite coupling pin undercompression, ant a graphite coupling pin frictionally engaged in saidsocket said pin being characterized by having a main body portioncoupled to said engaging portion and to an ex ternal power supply, saidengaging portion being in teriorly cut away to make it more pressurecompliant than said engaging portion would be if the interior cuttingwere absent, said cut away portion extending longitudinally from theface of the engaging portion in the direction of the main body portionand terminating within said graphite pin.

9. An electrical system according to claim 7 wherein the non-threadedsocket of the graphite anode is cylindrical in shape and wherein theengaging portion of the pin is of a general cylindrical shape flaredinto and integral with the main body portion of the pin, and chamferedat the peripheral edge of its face.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN COMBINATION, A GRAPHITE PIN ELECTRICALLY COUPLING AN EXTERNALPOWER SUPPLY TO AN ELECTRICAL CONDUCTING MEMBER HAVING A NON-THREADEDSOCKET RECEIVING AN ENGAGING PORTION OF SAID PIN UNDER COMPRESSION, SAIDPIN BEING CHARACTERIZED BY HAVING A MAIN BODY PORTION COUPLED TO SAIDENGAGING PORTION AND TO AN EXTERNAL POWER SUPPLY, SAID ENGAGING PORTIONBEING INTERIORLY CUT AWAY TO MAKE IT MORE PRESSURE COMPLIANT THAN SAIDENGAGING PORTION